CAP-HAIEN, Haiti - Hurricane Irma on Thursday pounded more of the Caribbean, shredding homes and weather records and leaving at least 12 people dead as it honed in on the United States, where up to a million people were told to flee.

The evacuation of coastal areas of Florida and neighboring Georgia was the biggest seen in the US in a dozen years.

"It will be truly devastating. The entire southeastern United States better wake up and pay attention," said Brock Long, head of the US Federal Emergency Management Agency.